Suggested materials to base my custom setting off of?

[A Butter Idea]

In the upcoming campaign I plan to GM, I am going to homebrew my own setting. I'm going to design the world as the campaign unfolds; I will provide a starting area that should suffice for 1st level, and then continuously design outwards depending on what the players decide to do. I've chosen this approach because the setting of Golarion just doesn't suit my needs. But I'm not confident in my ability to design towns and dungeons from scratch, so my plan is to buy some adventure paths, pick and choose the individual parts I like, and rearrange them into a cohesive whole.

Which adventure paths (or other sources) would likely have the kinds of things that would fit my campaign?

My homebrew setting is an Earth-like planet where humans are pretty much the only sapient Ancestry. If other Ancestries exist, they would all be very Rare. The starting area is largely modeled after Manhattan around the turn of the 20th century, with technology being partly steampunk, partly magitech. Culture and architecture can vary wildly compared to Earth's New York around that time, and can be ahead or behind the curve by plus-or-minus 30-40 years.

The Gilded Age is in full effect, and wage slavery is a major source of strife amongst the working class, mainly upheld by an aristocracy of wizards who have worked to slow the development of non-magical technology so that the working class remains reliant on them.

The city likely has many secrets buried beneath the surface, and the recent opening of the city's first subway line can be a great entry route for a dungeon or two. Additionally, there are some prominent commercial buildings which are as large as castles and up to 30 stories tall which the party may have to infiltrate on secret missions.

The existence of gods and the afterlife remains unconfirmed, but divine magic is about as commonplace as arcane magic, and faith in the ancient and storied traditions of their forebears allows clerics and champions to wield divine power.

Based on everything I laid out, which adventure paths or other sources would be most likely to have the best-fitting elements for my campaign, or at least the first few levels of it?

[QuidEst]

Magic: The Gathering's setting, New Capenna, will have plenty of roaring 20s fantasy art for you to use. Plenty of non-humans involved, though.

[A Butter Idea]

Actually, art assets are a low priority for me right now. I need prefabricated dungeon layouts, prefabricated town layouts, prefabricated scripted NPCs, and other things related to game mechanics. And I need all of these things to be designed for a setting that is within the ballpark of a turn-of-the-20th century urban setting, so that it's easy for me to reskin and rehash things as needed.

I think the Outlaws of Alkenstar adventure path is the most likely to have everything that I'm looking for, but I'd like for someone to confirm this for me first. If I drop money on a product, expecting to get things like street layouts wide enough for horseless carriage chases, industrialized factory floors, subway stations and tunnels, and tall office buildings designed for stealth missions; I would be very frustrated to find out that it just contains the usual medieval fantasy fare like dirt-road villages and castles and ancient ruins and whatnot.

I would also like to know if there are any other adventure paths besides Outlaws of Alkenstar published for PF2e that can be easily reskinned for an early 1900s big city adventure, if you happen to know of any.

[Loreguard]

It wouldn’t be second edition pathfinder, but you might find a lot of usable material for steampunk-esque setting if you look for material for the ZEITGEIST adventure path, which was a third party first edition adventure path if my memory is serving me.

If looking for some more modern maps you might look at some Starfinder materials. Many might be more futuristic than you want but others might feel more modern and you can ask your players to reskin the images in there minds to lower tech equivalent for things like desks and doors.

I’m trying to remember what starfinder adventure had the characters searching through a junkyard for something. Som starfinder scenarios might be able to have their tech scaled back some and still have a functional story.

I wonder if you could reskin Menace under Otari, and Trouble in Otari, into a steampunk setting.

Abomination Vault kind of highlights a lot of nonhumans so might be more work unless you turn the drow and moorlocks etc into underground mutants and such and have them exist. In your setting it isn’t entirely obvious what types of monsters exist.

But you might be able to replace one ancestry with a faction of humans relatively easily, for single sets like the kobolds under Otari.

[A Butter Idea]

I did check out Zeitgeist. While at a glance it did seem like it might be a good fit, closer examination revealed that it wouldn't have been a good fit at all.

I neglected to mention this in my previous posts, but the adventure I plan to run is one where the PCs become revolutionaries seeking to bring about justice through extralegal (and likely destructive) means. In Zeitgeist, the players work alongside law enforcement to bring known criminals to justice and ferret out doomsday conspirators that seek to totally upend the current status quo. By contrast, my adventure would necessarily bring the party into direct and frequent conflict with the local law enforcement, and they are going to be the ones upending a fundamentally corrupt system.

If anyone owns the Zeitgeist adventures, how easy (or difficult) do you think it would be to flip the script?

[Loreguard]

I wonder if that is a major flavor of your setting, I'm wondering if Hells Rebels would be something you might be able to extract some content out of. If I remember correctly, the first chapter had some of the earliest items that pulled the adventurers together was the players working to get money by collecting bounties on a excess of Giant Rats in the city, so the players were hunting them down for the reward money. I don't recall, but the search may have led them to information that led them to the plot-line. But I didn't get to play it so I can't tell you for sure. Perhaps someone here has played through it, and might be able to give you an estimation of how much of its plots could be easily reskinned to a more modern fantasy setting.

Perhaps you could look at Zeigeist support materials such as maps and such. I don't know if there are some on DriveThru.

I personally like some of Seafoot Games's maps so you might look at their Sci-Fi or their Towns & Cities maps if you need some for settings of encounters.

Actually, I also like Heroic Maps: you could potentially do a city encounter using tiles from their Free set Wardenhale Public Spaces or the rest of their Cities & Towns ones.

I'm sure there are other good maps there, those were just a couple sources that came to mind quickly to me.

You might also find some potential content if you look for content based in Razmiran. The very benevolent (ahem) divine leader of that nation Razmir has lots of detractors trying to cause problems for his benevolent plan for all of those who live under the rule of his most excellent nation. So troublemaking PCs might find themselves inclined to cause problems for the rightious establishment within its borders.

Ahem.... if you get my drift.

One of the scenarios in this free Quest is set in Rasmiran I believe:

The Silverhex Chronicles (Quest)

Here are a few Scenarios:
Lodge of the Living God
Killer in the Golden Maks
The Glass River Rescue

And a module:
Masks of the Living God (module)

But I believe all of them would need to be updated for second edition/remaster.

If you are interested in content for corruption within an evil nation, you might look at the recent Blood Lords AP. It is primarily a undead nation, with based on my understanding lots of ripe corruption within it. You might be able to convert some of the undead flavor into just massive amounts of corruption within a nation at war with another (probably equally corrupt nation). Or you could even have it be an undead nation if you allow that in in your primarily human fantasy setting. (having intelligent undead that were presumably once human)

Another setting with a basically evil, or perhaps more accurately chaotic regime of sorts would be Galt where there is constant revolutions. It might work well to have a neighboring nation beset by a chaotic revolution. It would give you a location nearby where factions can sprout, can vie for support, etc. But it can also be used by the evil establishment to point over there to its own populace, and say, see! This is what you get when you back Revolution, everyone gets hurt by it. We are after all the best of all possible options.

Following are some Adventures that a quick search says are set there.
Abducted in Aether
A Case of Missing Persons
Flight of the Red Raven
Forged Facade
Fury of the Final Blade
Night of the Gray Death
Reaping What We Sow
Requiem for the Red Raven

Sorry I can't give you absolute recommendations, but it is at least some brainstorming thoughts for things you can investigate if you don't get better leads on other specifics. Hope some of it helps.